The Association Between Trabecular Bone Score and Lumbar Spine Volumetric BMD Is Attenuated Among Older Men With High Body Mass Index

Abstract

Trabecular bone score (TBS) has been proposed as a dual-energy X-ray absorptiometry (DXA) derived measure of underlying quality of trabecular bone; however, TBS is not considered valid for those with body mass index (BMI) >37 kg/m2. Our objective was to determine the association between TBS and lumbar spine (trabecular) volumetric BMD (LS-VBMD) and to examine whether the association varied by BMI and body composition among older men below this clinical threshold. We used regression models to study 3479 men age ≥65 years enrolled in the Osteoporotic Fractures in Men (MrOS) study who had TBS from spine DXA scans, LS-VBMD from central quantitative computed tomography, measures of trunk fat and lean mass from DXA, and BMI <37kg/m2. TBS was categorized as normal (n = 925), partially degraded (n = 1747), and degraded (n = 807). TBS was inversely related to BMI, trunk fat mass, and trunk lean mass (all p< 0.001). The relationship between TBS and LS-VBMD was nonlinear with magnitude of effect (slope of regression line using standardized variables) ranging from 0.07 (95% CI, −0.02 to 0.15) among those with degraded TBS up to 0.71 (95% CI, 0.54 to 0.89) among those with normal TBS. The relationship was still nonlinear after adjusting for age, clinical site, and either BMI, trunk lean mass, or trunk fat mass. The magnitude of effect relating TBS and LS-VBMD also decreased with increasing BMI (interaction, p = 0.090) and increasing trunk lean mass (interaction, p = 0.001), but not with increasing trunk fat mass (interaction, p = 0.224). In summary, the strength of the association between TBS and LS-VBMD among older men was variable and dependent on BMI and body composition, particularly trunk lean mass. The clinical utility of TBS among older men may be somewhat limited among men with high BMI or high trunk lean mass.

Association of Trabecular Bone Score (TBS) With Incident Clinical and Radiographic Vertebral Fractures Adjusted for Lumbar Spine BMD in Older Men: A Prospective Cohort Study

“…We observed that the association between TBS and clinical vertebral fracture varied by BMI, being attenuated among those with higher BMI. This is consistent with the hypothesis that a larger thickness of soft tissue in front of and behind the lumbar spine may introduce more TBS measurement error and supported by our previous finding that the association of TBS with volumetric trabecular BMD measured with lumbar spine QCT becomes weaker as BMI increases …”

“…This is consistent with the hypothesis that a larger thickness of soft tissue in front of and behind the lumbar spine may introduce more TBS measurement error (10) and supported by our previous finding that the association of TBS with volumetric trabecular BMD measured with lumbar spine QCT becomes weaker as BMI increases. (4) In general, our results from MrOS are consistent with findings from the Manitoba Bone Density database as TBS in the latter study was not associated with incident clinical vertebral fractures in men after adjustment for lumbar spine BMD. In contrast, TBS has been shown to be associated with incident clinical vertebral fractures among women in the Manitoba cohort (11) and with incident radiographic vertebral fractures among women in the OPUS (12) and JPOS (13) studies, adjusted for both age and lumbar spine BMD.…”

Clinical Performance of the Updated Trabecular Bone Score (TBS) Algorithm, Which Accounts for the Soft Tissue Thickness: The OsteoLaus Study

“…The rationale behind these findings was that a higher skeleton load may cause an adaptive response of the bone, which may eventually result in better and stronger bones. We found, as reported previously, a negative association of TBS v3.03 with the body composition parameters . This paradoxical correlation has been explained with the possible artifactual effect that the regional presence of the soft tissue might have on the DXA scan.…”

“…We found, as reported previously, a negative association of TBS v3.03 with the body composition parameters. (12)(13)(14)(15)(16) This paradoxical correlation has been explained with the possible artifactual effect that the regional presence of the soft tissue might have on the DXA scan. Apparently, accounting for the BMI in the computational algorithm of TBS v3.03 could not completely overcome this technical issue; whereas the updated algorithm which accounts for the regional soft tissue thickness seems to deal with it.…”

“…To deal with this, the current algorithm for computing TBS accounts for the regional soft tissue thickness by using a surrogate for it, body mass index (BMI), because soft tissue thickness itself was not a widely and easily accessible measure . Studies have shown that TBS is negatively correlated with BMI or body weight, whereas BMD and bone biomechanical properties have been shown to be positively correlated with BMI or body weight . This negative correlation between TBS and BMI or weight could be due to the negative effect of excess fat on bone microarchitecture, or could be a technical limitation of TBS due to the regional soft tissue noise in the DXA image.…”